JPH10234175A - Gate drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To turn off a current-driven, self-arc-extinguishing semiconductor switching element in a shorter time than in conventional cases by supplying a steep and large off-gate current to the switching elements. SOLUTION: A second capacitor 8 is changed at a voltage, sufficiently higher than the charging voltage for a first capacitor 3. A first switching element 4 and a second switching element 9 are turned on, in accordance with an off command (off). Thus an off-gate current is supplied from the first capacitor 3 and the second capacitor 8 to a self-arc-extinguishing semiconductor element 1 in conduction for turning it off. When a turn-off signal A is output from a turn-off detecting means 11, the second switch 9 is turned off, independently of the off command to zero the off-gate current supplied from the second capacitor 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gate drive circuit for a current drive type self-extinguishing semiconductor switch element, and more particularly to a gate drive circuit improved so as to shorten a turn-off time.

[0002]

2. Description of the Related Art Gate turn-off thyristors (GTOs)
The current-driven self-extinguishing type semiconductor switch element represented by (1) is turned on (conducting) by a positive gate current (on-gate current) and turned off (non-conducting) by a negative gate current (off-gate current). This is known as a switching element having a current interruption function, and is generally used in a power converter for controlling a large power.

FIG. 9 shows a conventional gate drive circuit for supplying an off-gate current to a GTO, and a circuit for supplying an on-gate current is omitted because it is irrelevant to the present invention. In FIG. 9, when an off command (off) is given in a state where the GTO 1 is conducting and the anode current Ia is flowing between the anode and the cathode (AK), the switch element 4 is turned on (conducting) and the off-gate power supply is turned on. 2 discharges the charge of the capacitor 3 and supplies an off-gate current IRG between the gate and cathode (G-K) of the GTO 1;
GTO1 turns off and shifts to a non-conductive state.

In this case, in order to reliably turn off the GTO 1, it is necessary to supply an off-gate current IRG having a peak value obtained by dividing the anode current Ia by the turn-off gain.

For example, when an anode current Ia of 6000 A is flowing in a GTO having a turn-off gain of 5, 12
It is necessary to flow an off-gate current IRG having a peak value of 00A (6000A / 5). The off-gate current IRG is
The current flows through the capacitor 3 → the cathode (K) of the GTO1 → the gate (G) of the GTO1 → the switching element 4 → the capacitor 3; the current increase rate dIRG / dt of the off-gate current IRG is influenced by the floating inductance of this circuit.

FIG. 10 shows standard voltage and current waveforms when the GTO 1 is turned off.
3 shows a case where an off command (off) is given. That is, when the off command (off) is given at time t0 and the switch element 4 is turned on, the off-gate current IRG starts flowing at a current increase rate determined by the voltage of the off-gate power supply 2 and the stray inductance of the circuit, and the GTO at time t1.
1 indicates that the turn-off operation is started, the anode-cathode voltage Vak increases, the anode current Ia starts decreasing, and the turn-off operation is started.

When the GTO 1 starts to turn off at time t 1, a negative gate voltage (gate reverse voltage) V RG appears between the gate and cathode (G-K) of the GTO 1, the off-gate current I RG starts to decrease, and the turn-off operation starts. Upon completion, IRG will be zero.

The gate reverse voltage VRG is determined by the voltage of the off-gate power supply 2. When the switch element 4 is turned off at time t2, the gate reverse voltage VRG decreases to the gate reverse voltage VR0 divided by the resistors 5 and 6. The voltage Vak between the anode and the cathode slightly overshoots due to resonance phenomena such as an inductance (not shown) included in the main circuit and a capacitor of the snubber circuit in the process of completing the turn-off operation, and then becomes constant at the main circuit voltage.

When the GTO 1 is turned off, a characteristic of the Zener voltage Vz with respect to a reverse voltage of a predetermined voltage (about 20 V) appears between the gate and the cathode (G-K). If the voltage VRG of the gate power supply 2 is set higher than the zener voltage Vz, the off-gate current IRG continues to flow until the time t2 even after the turn-off operation is completed, so that not only the gate loss of the GTO1 increases but also the GTO may be damaged. For this reason, the gate reverse voltage VRG is usually designed to be lower than the Zener voltage Vz.

In the case of GTO, the period from time t0 to t1 is defined as the storage time, the period until the anode current Ia decreases to almost zero is defined as the fall time, and the sum of the two is defined as the turn-off time (turn-off time). I have.

[0011]

Generally, the turn-off time of the GTO is about 20 to 30 μs.
It has been found that if the turn-off gain is reduced by improving the TO structure and an off-gate current having a peak value close to the rapidly rising anode current is supplied, the turn-off time is shortened to about 1/10 of the conventional case. For example, the current increase rate (dIRG / dt) of the off-gate current IRG is 2000 A / μ
It has been found that when an off-gate current having a peak value of 3000 to 4000 A is supplied in s, an anode current of 3000 to 6000 A is turned off in 2 to 3 μs.

In this case, the current increase rate of the off-gate current IRG is 2000 A / μs and the peak value is 3000 to 4000.
It is necessary to supply a larger off-gate current A, which is steeper than before. For example, if the off-gate voltage VRG is equal to the normal 2
To make the current rise rate 2000 A / μs at 0 V,
The floating inductance of the gate circuit through which the off-gate current flows is 10 nH (20 V / 10 nH = 2000 A / μs)
It is necessary to

However, in the current state of the art, several thousand A
The stray inductance of a gate circuit through which an off-gate current for controlling the main circuit current flows is physically about 100 nH, and it is difficult to reduce the stray inductance to a value less than about 100 nH.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to supply a steep and large off-gate current to a current-driven self-extinguishing semiconductor switch element so that a shorter time than in the past can be achieved. And to provide a gate drive circuit for turning off.

[0015]

To achieve the above object, the gate drive circuit of the present invention is configured as follows. (Claim 1) A first capacitor and a second capacitor for supplying an off-gate current for turning off a self-extinguishing type semiconductor element in an energized state;
A first switch element and a second switch element to be turned off, and turn-off detection means for judging a turn-off state of the self-extinguishing semiconductor element and outputting a turn-off signal;
The second capacitor is charged at a voltage sufficiently higher than the charging voltage of the first capacitor, and the first capacitor is charged based on an OFF command.
Turning on a switch element and a second switch element, supplying an off-gate current from the first capacitor and the second capacitor, and turning off the second switch regardless of the off command when the turn-off signal is output; Off-gate current supplied from the

The present invention further comprises a current detecting means for detecting an anode current of the self-extinguishing semiconductor device, wherein the second capacitor is charged at a voltage sufficiently higher than a charging voltage of the first capacitor. When the anode current is equal to or less than a predetermined value, the first switch element is turned on based on the off command, an off-gate current is supplied from the first capacitor, and when the anode current exceeds a predetermined value, based on the off command. To turn on the first switch element and the second switch element to supply an off-gate current from the first capacitor and the second capacitor, and to turn off the second switch when the turn-off signal is output irrespective of the off command. , The off-gate current supplied from the second capacitor is set to zero.

(3) The charging voltage of the first capacitor is lower than a Zener voltage with respect to a reverse voltage between the gate and the cathode of the self-extinguishing semiconductor device, and the charging voltage of the second capacitor is the Zener voltage. Charge to a voltage higher than the voltage.

(Claim 4) Further, after a predetermined time from when the off command is given, the second switch is turned off irrespective of the turn-off signal, and continuous operation can be performed even if the turn-off detecting means fails. .

(5) The turn-off detecting means detects the reverse voltage by insulating the reverse voltage via a photocoupler, and outputs the turn-off signal when the reverse voltage exceeds a predetermined value.

(7) The turn-off detecting means further detects the anode voltage or the charging voltage of the capacitor of the snubber circuit through a photocoupler and detects the anode voltage or the charging voltage of the snubber circuit. The turn-off signal is output when the charging voltage of the capacitor exceeds a predetermined value.

(10) The turn-off detecting means outputs the turn-off signal when the anode current of the self-extinguishing type semiconductor device becomes equal to or less than a predetermined current.

(11) The turn-off detection means outputs the turn-off signal when a current flowing through a snubber circuit of the self-extinguishing semiconductor device becomes equal to or more than a predetermined current.

[0023]

FIG. 1 shows an embodiment of a gate drive circuit according to the present invention. In FIG. 1, 7 is a gate power supply having a voltage sufficiently higher (for example, about 10 times) than the voltage of the gate power supply 2, 8 is a capacitor charged by the gate power supply 7, 9 is a switch element, 10 is an AND circuit, and 11 is G
This is a turn-off detection circuit that outputs an off signal A when the turn-off completion timing of TO1 is determined. The other components are the same as those of the related art (FIG. 10), and are denoted by the same reference numerals.

The turn-off detection circuit 11 normally outputs an off signal A having a logical value of 1, and has the function of inverting the logical value of the off signal A from 1 to 0 when it is determined that the turn-off of the GTO 1 is completed.

In the above configuration, when an off command (off) is given while the GTO 1 is conducting and the anode current Ia is flowing, the switching elements 4 and 9 are simultaneously turned on (conducting), and the off-gate power supply 2 is turned off. The charge of the capacitor 3 charged by the GTO1 is discharged, the charge of the capacitor 8 charged by the off-gate power supply 7 is discharged, and both discharge currents are added between the gate and the cathode (G-K) of the GTO1. An off-gate current IRG having a larger peak value at a steep rise than before is supplied. When the turn-off operation of the GTO 1 is completed by the off-gate current IRG, the logic value of the off signal A output from the off detection circuit 11 changes from 1 to 0, the gate of the AND circuit 10 is closed, and the switch element 9 is turned off. As a result, the discharge current from the capacitor 8 is set to zero, and only the discharge current from the capacitor 3 is used.

Therefore, until the GTO 1 completes the turn-off operation, the off-gate current I RG having a sharp peak and a large peak value is supplied. FIG. 2 shows voltage and current waveforms at the time of turn-off operation of the present embodiment, and shows a case where an off command (off) is given from time t0 to t3.

Since the charging voltage VRG2 of the capacitor 8 is sufficiently higher than the charging voltage VRG1 of the capacitor 3, the current increase rate (dIRG / dt) of the off-gate current IRG is substantially determined by the charging voltage VRG2 of the capacitor 8. In this case, the current increase rate (dIRG / dt) of the off-gate current IRG is expressed by equation (1).

[0028]

DIRG / dt = VRG2 / L [A / s] (1) where VRG2 is the charging voltage [V] of the capacitor 8, and L is the stray inductance [H] of the circuit. Therefore, the stray inductance of the circuit that can be realized is L = 0.1 [μH]
For example, if V RG2 = 200 [V],

[0029]

## EQU2 ## dIRG2 / dt = 200 / 0.1 = 2000 [A / .mu.s] (2) The off-gate current IRG2 with a steep rising reaching 4000 A in 2 .mu.s is obtained. FIG. 2 shows an example in which the off-gate current IRG of the sum (IRG1 + IRG2) of the off-gate current IRG2 and the off-gate current IRG1 supplied from the capacitor 3 is supplied to the GTO1 from time t0.

The GTO1 starts a turn-off operation, and at time t2, the anode current Ia decreases to almost zero, the off-detection circuit 11 determines the completion of the turn-off of the GTO1, and changes the logic value of the off signal A from 1 to 0. And off command (of
Even when f) is given, the gate of the AND circuit 10 is closed, the switch element 9 is turned off, and the off-gate current IRG2 supplied from the capacitor 8 decreases rapidly to zero.
Therefore, the off-gate current I supplied from the capacitor 3
Only RG1.

It should be noted that the voltage of the gate power supply 2 is
The gate power supply 7 is set to be equal to or lower than the zener voltage Vz between
Is set to be equal to or higher than the Zener voltage Vz. With this setting, the off-gate current IRG1 can be gradually reduced to zero, and the gate power loss of the GTO1 is reduced. (Claim 3) If the turn-off detection circuit 11 fails and the logic value of the turn-off signal A does not invert from 1 to 0, the high voltage VRG2 charged in the capacitor 8 is continuously applied. Large off-gate current IRG as shown by the dotted line 2
2 continues to flow until time t3, exceeding the allowable gate power loss of GTO1 and risking damage to GTO1.

In order to prevent this danger, an off command (off
) Can be provided with a timer 18 which closes the gate of the AND circuit 10 a predetermined time after the time t0 at which the signal is given. The predetermined time is set slightly longer than the maximum turn-off time specified based on the rating of the GTO. With this setting, the turn-off detection circuit 11
Even if a failure occurs, the off-gate current IRG2 can be reliably reduced to zero after a lapse of a predetermined time, and the operation can be continued without damaging the GTO. (Claim 4) Further, according to the present invention, as shown in FIG. 3, a current detector 12 for detecting an anode current Ia of the GTO 1 and a signal B when the detected anode current Ia is equal to or less than a predetermined current. An output current level determiner 13 is provided. When the anode current Ia is equal to or less than a predetermined current, the gate of the AND circuit 10 is closed by the signal B, and the switch element 9 is not turned on even when an off command (off) is given. You can do so.

In this case, the predetermined current is the value of the capacitor 3
Value of off-gate current IRG supplied from
It is set to a value determined by a turn-off gain of 1 (sufficiently smaller than the rated current), and is set so as to be surely turned off only by the off-gate current IRG1.

According to this embodiment, the gate power loss can be reduced and the operation efficiency can be improved in light load operation in which the anode current of the GTO is equal to or less than a predetermined current. (Claim 2) FIG. 4 shows a specific embodiment of the turn-off detection circuit 11.

That is, a series circuit of the resistor 14 and the Zener diode 15 is connected between G and K of the GTO 1,
When O1 is turned off and a reverse voltage VRG is generated between G and K, if the reverse voltage VRG exceeds the Zener voltage of the Zener diode 15, a current corresponding to the reverse voltage VRG flows through the resistor 14 and a voltage drop Vx occurs. When the voltage drop Vx exceeds a predetermined voltage, the voltage level detector 16
1 to determine the completion of turn-off, and output a turn-off signal A. (Claim 5) Further, as shown in FIG.
Is connected between G-K of GTO1.
When the reverse voltage VRG becomes equal to or higher than a predetermined voltage, the light receiving element of the photocoupler 17 may be turned on to output a turn-off signal A. Further, as shown in FIG. 6, resistors 19 and 20 for dividing the anode voltage between A and K of the GTO 1 and a voltage for outputting a turn-off signal A when the divided voltage exceeds a predetermined voltage. The level detector 21 may be provided to output the turn-off signal A when the anode voltage exceeds a predetermined value. (Claim 7) As shown in FIG. 7, a resistor 2 is connected between A and K of GTO1.
2 is connected to a series circuit of the light emitting diode 23, and when the anode voltage exceeds a predetermined value, the light receiving element 25 is turned on by an optical signal output from the light emitting diode 23, and a turn-off signal A is output. Can also. 24 is a diode for preventing a reverse voltage applied to the light emitting diode 25, 26 is a knot circuit, and 27 is a resistor. According to this embodiment, the anode voltage can be detected while insulated by the optical fiber 28. (Claim 9) As in FIG. 3, a circuit for determining the level of the anode current of the GTO1 is provided, and when the anode current falls below a predetermined current close to zero, a turn-off signal A is output. You can also. (Claim 10) As shown in FIG. 8A, a surge current Is flowing through a snubber circuit connected between A and K of the GTO 1 is detected by a current detector 33, and the surge current Is is set to a predetermined level. May be detected by the current level determiner 34 to output the turn-off signal A. The snubber circuit includes a diode 30, a capacitor 31, and a resistor 32. (Claim 11) As shown in FIG. 8 (b), the surge current Is increases so that the anode current Ia is commutated to the snubber circuit to complement the decrease in the anode current Ia, and accumulates in the inductance of the main circuit (not shown). It flows until the discharged current becomes zero.
Further, the surge current Is flows as a charging current for the snubber capacitor 31, and the voltage of the snubber capacitor 31 rises rapidly and becomes constant at the AK voltage Vak of the GTO1. Therefore, when the charging voltage of the snubber capacitor 31 exceeds a predetermined value, the turn-off signal A may be output. In this case, it can be insulated by a photocoupler or the like as described above (FIG. 7). (Claim 9) Although FIG. 1 shows an example in which the gate power supply 2 and the gate power supply 7 are separately provided, the gate power supply 2 and the gate power supply 7 may be configured as one gate power supply having the intermediate potential VRG1 at the voltage VRG2.

[0036]

According to the gate drive circuit of the present invention, a very large off-gate current is supplied until the turn-off is completed.
After the turn-off is completed, the current can be switched to the normal off-gate current, so that the turn-off time can be shortened without significantly increasing the gate power loss of the self-turn-off semiconductor device, and the modulation frequency of the PWM control can be reduced. The off-gate current can be reduced for light load operation, and efficient operation can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a gate drive circuit of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment.

FIG. 3 is a configuration diagram of a main part of an embodiment according to claim 2 of the present invention.

FIG. 4 is a configuration diagram of a main part of an embodiment according to claim 5 of the present invention.

FIG. 5 is a configuration diagram of a main part of an embodiment according to claim 6 of the present invention.

FIG. 6 is a configuration diagram of a main part of an embodiment according to claim 7 of the present invention.

FIG. 7 is a configuration diagram of a main part of an embodiment according to claim 8 of the present invention.

FIG. 8 is a configuration diagram and a waveform diagram of a main part of an embodiment according to claim 11 of the present invention.

FIG. 9 is a configuration diagram of a conventional gate drive circuit.

FIG. 10 is a waveform chart for explaining the operation of a conventional gate drive circuit.

[Description of Signs] 1 Self-extinguishing semiconductor device (GTO) 2 Gate power supply 3 Capacitor 4 Switch element 5, 6 Resistor 7 Gate power supply 8 Capacitor 9 Switch element 10 AND circuit 11 Turn-off detection circuit 12 ... Current detector 13 ... Current level determiner 14, 18-20, 22 ... Resistor 15 ... Zener diode 16, 21 ... Voltage level determiner 17 ... Photocoupler 23 ... Light emitting element 24 ... Diode 25 ... Light Receiving element 26 Knot circuit 28 Optical fiber 30 Diode 31 Capacitor 32 Resistor 33 Current detector 34 Current level determiner

Claims (11)

[Claims] A first capacitor and a second capacitor for supplying an off-gate current for turning off a self-extinguishing type semiconductor device in an energized state, and an on / off switch based on an off command.
A first switch element and a second switch element to be turned off, and turn-off detection means for judging a turn-off state of the self-extinguishing semiconductor element and outputting a turn-off signal;
The second capacitor is charged at a voltage sufficiently higher than the charging voltage of the first capacitor, and the first capacitor is charged based on an OFF command.
Turning on the switch element and the second switch element,
An off-gate current is supplied from a capacitor and a second capacitor, and when the turn-off signal is output, the second switch is turned off irrespective of the off command, and the off-gate current supplied from the second capacitor is set to zero. Gate drive circuit. 2. A first capacitor and a second capacitor for supplying an off-gate current for turning off a self-extinguishing type semiconductor element in an energized state, and an on / off switch based on an off command.
A first switch element and a second switch element to be turned off, current detecting means for detecting an anode current of the self-extinguishing type semiconductor element, and a turn-off signal by judging a turn-off state of the self-extinguishing type semiconductor element; Turn-off detecting means for charging the second capacitor at a voltage sufficiently higher than the charging voltage of the first capacitor, and turning on the first switch element based on the off command when the anode current is equal to or less than a predetermined value. An off-gate current is supplied from the first capacitor, and when the anode current exceeds a predetermined value, the first switch element and the second switch element are turned on based on the off command, and the first capacitor and the second capacitor are turned on. An off-gate current is supplied from a capacitor, and when the turn-off signal is output, the second switch is independent of the off command. Ji was off, the gate drive circuit, characterized in that the off-gate current supplied from the second capacitor to zero. 3. The gate drive circuit according to claim 1, wherein a charging voltage of the first capacitor is lower than a Zener voltage for a reverse voltage between a gate and a cathode of the self-extinguishing semiconductor device. A gate drive circuit that charges the second capacitor to a voltage equal to or higher than the Zener voltage. 4. The gate drive circuit according to claim 1, wherein the second switch is turned off irrespective of the turn-off signal a predetermined time after a time point when an off command is given, and A gate drive circuit characterized in that continuous operation is possible even if a failure occurs. 5. The gate drive circuit according to claim 1, wherein said turn-off detection means outputs said turn-off signal based on a reverse voltage generated between a gate and a cathode of said self-extinguishing semiconductor device. A gate drive circuit characterized in that: 6. The gate drive circuit according to claim 5, wherein said turn-off detecting means detects and insulates said reverse voltage and outputs said turn-off signal when said reverse voltage exceeds a predetermined value. Gate drive circuit. 7. The gate drive circuit according to claim 1, wherein said turn-off detecting means outputs said turn-off signal based on an anode voltage generated between an anode and a cathode of said self-extinguishing type semiconductor device. A gate drive circuit characterized in that: 8. The gate drive circuit according to claim 1, wherein said turn-off detection means outputs said turn-off signal based on a charging voltage of a capacitor of said snubber circuit. circuit. 9. The gate drive circuit according to claim 7, wherein said turn-off detection means insulates and detects said anode voltage or a charging voltage of a capacitor of said snubber circuit, and detects said anode voltage or said anode voltage. A gate drive circuit for outputting the turn-off signal when a charging voltage of a capacitor of a snubber circuit exceeds a predetermined value. 10. The gate drive circuit according to claim 1, wherein said turn-off detection means outputs said turn-off signal when an anode current of said self-extinguishing type semiconductor element becomes equal to or less than a predetermined current. A gate drive circuit, characterized in that: 11. The gate drive circuit according to claim 1, wherein said turn-off detecting means is configured to output said turn-off signal when a current flowing through a snubber circuit of said self-extinguishing semiconductor device becomes equal to or greater than a predetermined current. A gate drive circuit, which outputs a signal.